Zoom lens and imaging apparatus

ABSTRACT

A zoom lens substantially consists of, in order from the object side, a positive first lens group, a negative second lens group, a positive third lens group, a positive fourth lens group, and a negative fifth lens group. When varying magnification, the distances between adjacent lens groups) are changed, while all of the lens groups are moved with respect to an image formation position. When focusing, only the fifth lens group is shifted, and the third lens group has a third-a lens group having positive refractive power and a third-b lens group having negative refractive power, which are arranged in this order from the object side, only the third-b lens group is moved in a direction perpendicular to the optical axis to achieve camera shake correction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens having a high variable magnification ratio used in electronic cameras such as digital cameras, video cameras, broadcasting cameras, surveillance cameras and the like, to a zoom lens having a camera shake correction function, and to an imaging apparatus including the zoom lens.

2. Description of the Related Art

Conventionally, a zoom lens substantially consisting of: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; a fourth lens group having positive refractive power; and a fifth lens group having negative refractive power, which are arranged in this order from the object side, is known as a zoom lens having relatively a high variable magnification ratio. The zoom lens with such a lens construction is known to be appropriate for realizing both a high variable magnification ratio and a reduction in size (see Japanese Unexamined Patent Publication No. 4 (1992)-070707, U.S. Pat. No. 5,872,659, and Japanese Unexamined Patent Publication No. 11 (1999)-064728)

As a zoom lens having “a camera shake correction function (a vibration-proof function)” for preventing image blurring attributed to vibration, camera shake and the like, a zoom lens that substantially consists of a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, arranged in this order from the object side, the third lens group of which comprises two groups, a partial group having positive refractive power and a partial group having negative refractive power, and that exhibits camera shake correction effects by moving the partial group having negative refractive power in a direction perpendicular to an optical axis, is known (see U.S. Pat. No. 6,462,885).

SUMMARY OF THE INVENTION

Recently, there is demand for a zoom lens, which has a camera shake correction function and is compact, and yet has a high variable magnification ratio, e.g., a zoom lens which has a high variable magnification ratio of over 12×, and yet which is compact and capable of high performance.

However, conventionally known compact and high performance zoom lenses, e.g., the zoom lenses disclosed in see Japanese Unexamined Patent Publication No. 4 (1992)-070707, U.S. Pat. No. 5,872,659, and Japanese Unexamined Patent Publication No. 11 (1999)-064728, have variable magnification ratios of less than 10×, and cannot necessarily be said to have high variable magnification ratios.

The present invention has been developed in view of the foregoing circumstances. It is an object of the present invention to provide a zoom lens, which has a high variable magnification ratio, and yet which is compact, capable of high performance, and has a camera shake correction function, as well as an imaging apparatus including the zoom lens.

A zoom lens of the present invention substantially consists of:

a first lens group having positive refractive power;

a second lens group having negative refractive power;

a third lens group having positive refractive power;

a fourth lens group having positive refractive power; and

a fifth lens group having negative refractive power, which are arranged in this order from an object side,

wherein when varying magnification from a wide angle end to a telephoto end, the distance between the first lens group and the second lens group is consistently increased, the distance between the second lens group and the third lens group is consistently decreased, the distance between the third lens group and the fourth lens group is consistently decreased, and the distance between the fourth lens group and the fifth lens group is changed, while all of the lens groups are moved with respect to an image formation position,

wherein when moving a point of focus from an infinity side to a near side to achieve focus, only the fifth lens group is moved from the object side to the image side,

the third lens group comprises a third-a lens group having positive refractive power and a third-b lens group having negative refractive group, which are arranged in this order from the object side, and

only the third-b lens group is moved in a direction perpendicular to the optical axis to achieve camera shake correction.

The zoom lens may substantially consist of five lens groups. In this case, the expression “zoom lens which substantially consists of n lens groups” refers to a zoom lens that includes lenses substantially without any refractive power; optical elements other than lenses such as apertures and glass covers; and mechanical components such as lens flanges, lens barrels, imaging elements, and camera shake correction mechanisms; in addition to the n lens groups.

Further, it is desirable for the zoom lens 100 to satisfy formula (M): −2.00<f_(3a)/f_(3b)<−0.85, and more desirably, formula (M′): −1.00<f_(3a)/f_(3b)<−0.85, where f_(3a) is the focal length of the third-a lens group 3Ga, and f_(3b) is the focal length of the third-b lens group 3Gb.

The third-b lens group 3Gb may substantially consist of one negative lens and one positive lens.

The third-b lens group 3Gb can be composed of two single lenses and at least one surface can be an aspheric lens.

An imaging apparatus of the present invention is equipped with the zoom lens of the present invention.

The zoom lens and the imaging apparatus including the zoom lens according to the present invention substantially consist of:

a first lens group having positive refractive power;

a second lens group having negative refractive power;

a third lens group having positive refractive power;

a fourth lens group having positive refractive power; and

a fifth lens group having negative refractive power, which are arranged in this order from the object side of the zoom lens,

wherein when varying magnification from a wide angle end to a telephoto end, the distance between the first lens group and the second lens group is consistently increased, the distance between the second lens group and the third lens group is consistently decreased, the distance between the third lens group and the fourth lens group is consistently decreased, and the distance between the fourth lens group and the fifth lens group is changed such that all of the lens groups moved with respect to an image formation position,

wherein when moving a point of focus from an infinity side to a near side to achieve focus, only the fifth lens group is moved from the object side to the image side,

wherein the third lens group comprises a third-a lens group having positive refractive power and a third-b lens group having negative refractive power, which are arranged in this order from the object side, and

only the third-b lens group is moved in a direction perpendicular to the optical axis so as to achieve camera shake correction, thereby enabling the zoom lens to have a high variable magnification ratio, and yet to be compact, be capable of high performance and have a camera shake correction function.

Thus, for example, a zoom lens which has a full angle of view at a wide angle end exceeding 75°, that is, a large angle of view, and which further has a high variable magnification ratio exceeding 12×, and yet is compact, capable of high performance, and has a camera shake correction function, can be configured.

More specifically, the zoom lens of the present invention configured as described above can facilitate suppression of performance variations in the zoom intermediate range, compared to conventionally known zoom lenses (a zoom lens that is constituted of four lens groups: a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, which are arranged in this order from the object side).

Further, when changing focusing positions from the infinity side toward the near side, only the fifth lens group is moved from the object side to the image side. This enables a reduction in size and weight of the focusing group (the fifth lens group 5G), thereby reducing the burden on a focus mechanism, and realizing high-speed focus.

Further, the camera shake correction can be carried out by moving only the third-b lens group that constitutes the third lens group in a direction perpendicular to the optical axis, which enables reducing a diameter of luminous flux by positive refractive power of the third-a lens group before transmitting this luminous flux through the third-b lens group. Thereby, the effective diameter of the third-b lens group can be small, which can reduce a weight of a camera shake correction group (the third-b lens group). This can realize a reduction in the burden on the camera shake correction mechanism for enabling the movement of the third-b lens group in a direction perpendicular to the optical axis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional diagram illustrating the structure of a zoom lens and an imaging apparatus including the zoom lens according to an embodiment of the present invention;

FIG. 2A is a cross sectional diagram illustrating a zoom lens of Example 1;

FIG. 2B is a cross sectional diagram illustrating each of a case that a zoom setting of the zoom lens of Example 1 is set to a wide angle end and a case that a zoom setting thereof is set to a telephoto end;

FIG. 3A is a cross sectional diagram illustrating a zoom lens of Example 2;

FIG. 3B is a cross sectional diagram illustrating each of a case that a zoom setting of the zoom lens of Example 2 is set to the wide angle end and a case that a zoom setting thereof is set to the telephoto end;

FIG. 4A is a cross sectional diagram illustrating a zoom lens of Example 3;

FIG. 4B is a cross sectional diagram illustrating each of a case that a zoom setting of the zoom lens of Example 3 is set to the wide angle end and a case that a zoom setting thereof is set to the telephoto end;

FIG. 5A is a cross sectional diagram illustrating a zoom lens of Example 4;

FIG. 5B is a cross sectional diagram illustrating each of a case that a zoom setting of the zoom lens of Example 4 is set to the wide angle end and a case that a zoom setting thereof is set to the telephoto end;

FIG. 6A is a cross sectional diagram illustrating a zoom lens of Example 5;

FIG. 6B is a cross sectional diagram illustrating each of a case that a zoom setting of the zoom lens of Example 5 is set to the wide angle end and a case that a zoom setting thereof is set to the telephoto end;

FIG. 7 is an aberration diagram of Example 1;

FIG. 8 is an aberration diagram of Example 2;

FIG. 9 is an aberration diagram of Example 3;

FIG. 10 is an aberration diagram of Example 4; and

FIG. 11 is an aberration diagram of Example 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the zoom lens ad the imaging apparatus including the lens of the present invention will be described with reference to the attached drawings.

FIG. 1 is a schematic cross sectional diagram illustrating the structure of a zoom lens and an imaging apparatus including the zoom lens according to an embodiment of the present invention.

The zoom lens 100 as shown in the Figure has a high variable magnification ratio, and yet is compact, capable of high performance, and has a camera shake correction function. The imaging apparatus 200 equipped with the zoom lens 100 is used as a digital still camera, a video camera, a surveillance camera, or the like.

The zoom lens 100 comprises a first lens group 1G having positive refractive power, a second lens group 2G having negative refractive power, a third lens group 3G having positive refractive power, a fourth lens group 4G having positive refractive power, and a fifth lens group 5G having negative refractive power, in this order from an object side (the side of −Z in the Figures).

The zoom lens 100 consistently increases a distance δ12 between the first lens group 1G and the second lens group 2G, consistently decreases a distance δ23 between the second lens group 2G and the third lens group 3G, consistently decreases a distance δ34 between the third lens group 3G and the fourth lens group 4G, and changes a distance δ45 between the fourth lens group 4G and the fifth lens group 5G, while all of the lens groups 1G through 5G are moved with respect to an image formation surface Mk which is an image formation position of the zoom lens 100, when zooming from the wide angle end to the telephoto end (continuously varying magnification).

Further, the above zoom lens 100 is designed to move only the fifth lens group 5G to the image side to achieve focus when moving a point of focus from an infinity side to a near side. The third lens group 3G is constructed to have a third-a lens group 3Ga having a positive refractive power and a third-b lens group 3Gb having a negative refractive power, in this order from the object side, and to move only the third-b lens group 3Gb in a direction perpendicular to an optical axis, which enables a camera shake correction function to work.

The direction perpendicular to the optical axis refers to a direction which is perpendicular to the optical axis Z1, and a direction in which an X-Y plane extends.

In such a manner, the basic configuration of the zoom lens 100 is described above.

Further, it is desirable for the zoom lens 100 to satisfy formula (M): −2.00<f_(3a)/f_(3b)<−0.85, and more desirably, formula (M′): −1.00<f_(3a)/f_(3b)<−0.85, where f_(3a) is the focal length of the third-a lens group 3Ga, and f_(3b) is the focal length of the third-b lens group 3Gb.

Formula (M) regulates the ratio of the focal length of the third-a lens group 3Ga to the focal length of the third-b lens group 3Gb. If the zoom lens 100 is constructed in such a manner that the value of f_(3a)/f_(3b) is lower than the lower limit defined by formula (M), the negative refractive power of the third-b lens group 3Gb will excessively increase, so that the amount of shift of the third-b lens group 3Gb in a direction perpendicular to the optical axis, which is necessary for the camera shake correction, will be excessively reduced. This will cause a problem that it becomes difficult to control the camera shake correction group (the third-b lens group 3Gb) against micro-vibration. If the zoom lens is constructed in such a manner that the value of f_(3a)/f_(3b) exceeds the upper limit defined by formula (M), the negative refractive power of the third-b lens group 3Gb will be diminished and the amount of shift of the third-b lens group 3Gb necessary for the camera shake correction will be excessively increased, which causes a problem that a size of the camera shake correction mechanism will become great.

It is desirable for the third-b lens group 3Gb of the zoom lens 100 to substantially consist of one negative lens and one positive lens. This enables correcting eccentric chromatic aberration which occurs at the time of correcting the camera shake, while achieving a reduction in a weight of the third-b lens group 3Gb, thereby reducing the burden on the camera shake correction mechanisms.

Further, it is desirable for the third-b lens group 3Gb to substantially consist of two single lenses and for at least one surface to have an aspheric lens. This enables correcting eccentric comatic aberration which occurs at the time of the camera shake correction, while maintaining a good optical performance.

The imaging apparatus 200 illustrated in FIG. 1 includes the zoom lens 100, and an imaging element 210 constituted of a CCD which images an optical image Hk (an optical image representing a subject H) formed through the zoom lens 100, a CMOS, or the like. An imaging surface 211 of the imaging element 210 is an image formation position (an image formation surface Mk) of the imaging lens 100.

In this case, an optical member Dg is disposed between the most-image-side lens (as indicated by the item Se in the zoom lens 100 of FIG. 1) and the imaging surface 211.

Various optical members may be employed as the optical member Dg depending on the configuration of the imaging apparatus 200 with which the imaging lens 100 is equipped. For example, a single or a plurality of a member or members that correspond(s) to an imaging surface protection cover glass, an infrared cut filter, an ND filter, and the like may be provided.

Hereinafter, Examples 1 through 5 of the zoom lens of the present invention will be specifically described with reference to FIGS. 2A, 2B . . . 6A, 6B, 7 . . . 11 and the like.

Each zoom lens of Examples 1 through 5 satisfies the configuration of the zoom lens 100 and includes the following constituent elements.

Each zoom lens of Examples 1 through 5 is constituted by a first lens group 1G consisting of three lenses, a second lens group 2G consisting of four lenses, a third lens group 3G consisting of five lenses, a fourth lens group 4G consisting of three lenses, and a fifth lens group 5G consisting of two lenses.

In the first lens group 1G, a first group-first lens L1, a first group-second lens L2, and a first group-third lens L3 are arranged in this order from the object side.

Further, in the second lens group 2G, a second lens group-first lens L4, a second lens group-second lens L5, a second lens group-third lens L6, and a second lens group-fourth lens L7 are arranged in this order from the object side.

Further, in the third lens group 3G, a third lens group-first lens L8, a third lens group-second lens L9, a third lens group-third lens L10, a third lens group-fourth lens L11, and a third lens group-fifth lens L12 are arranged in this order from the object side.

In the fourth lens group 4G, a fourth lens group-first lens L13, a fourth lens group-second lens L14, and a fourth lens group-third lens L15 are arranged in this order from the object side.

Further, in the fifth lens group 5G, a fifth group-first lens L16 and a fifth group-second lens L17 are arranged in this order from the object side.

The third lens group 3G substantially consisting of five lenses as described above, is constructed to have three lenses (a third-a lens group 3aG having positive refractive power) arranged closest to the object side and two lenses arranged closest to the image side (a third-b lens group 3bG). The third-b lens group 3bG is constructed to be movable in a direction perpendicular to an optical axis (a direction in which an X-Y plane extends), which enables a camera shake correction function to work.

In this case, the third-a lens group 3aG substantially consists of the third group-first lens L8, the third group-second lens L9, and the third group-third lens L10, and the third-b lens group 3bG substantially consists of the third group-fourth lens L11 and the third group-fifth lens L12.

An aperture stop St is disposed between the second lens group 2G and the third lens group 3G and is designed to be moved in an optical axis direction Z1 integrally with the third lens group 3G at the time of varying magnification.

EXAMPLE 1

FIGS. 2A and 2B illustrate a zoom lens of Example 1. FIG. 2A is a detailed diagram illustrating the configuration of the zoom lens of Example 1. FIG. 2B illustrates a state in which the zoom setting of the zoom lens of Example 1 is set to the wide angle end (as indicated by “WIDE” in the Figure) at the upper part and a state in which the zoom setting thereof is set to the telephoto end (as indicated by “TELE” in the Figure) at the bottom part. Further, arrows indicate the paths of movement of the lens groups, respectively when magnification is changed from the wide angle end to the telephoto end.

In the fifth lens group 5G of the zoom lens of Example 1, two lenses, i.e., a negative lens and a positive lens, are arranged in this order from the object side.

Further, Table 1A to be described later shows various data related to the zoom lens of Example 1. The upper part of Table 1A shows lens data, the middle part shows schematic specifications of the zoom lens, and the bottom part shows the focal length of each lens group.

In the lens data at the upper part of Table 1A, a surface number represents the i-th (i=1, 2, 3, . . . ) lens surface or the like, and the number sequentially increases from the most-object side toward the image side. The aperture stop St and the optical member Dg are also listed in these lens data.

Radius Ri of curvature represents the radius of curvature of the i-th surface (i=1, 2, 3, . . . ). Distance Di between surfaces (i=1, 2, 3, . . . ) represents the distance between the i-th surface and an (i+1)th surface on the optical axis Z1. The item Ri and the item Di in the lens data correspond to the item Si (i=1, 2, 3, . . . ) representing a lens surface or the like.

In the column of distance Di between surfaces (i=1, 2, 3, . . . ), there are a case in which numeral values representing the distance between surfaces are listed and a case in which the item Dm (m is an integral number). Numbers in the item Dm correspond to distances between surfaces (spatial distances), between the lens groups, and the distance between surfaces (spatial distance) varies depending on variable magnification ratios (zoom magnification).

Further, the item Nj represents the refractive index of a j-th (j=1, 2, 3, . . . ) optical element with respect to wavelength of 587.6 nm (the d-line), and numbers sequentially increase from the object side toward the image side. The item νj represents the Abbe number of the j-th optical element based on the d-line.

In the lens data of Table 1A, the unit of the radius of curvature and the distances between surfaces is mm. The radius of curvature is positive when a convex surface faces the object side and is negative when a convex surface faces the image side.

The optical system as described above is generally capable of maintaining a predetermined performance level in any of cases where the size of optical elements such as a lens or the like is proportionately increased or decreased, and therefore zoom lenses in which the numbers of the entire lens data are proportionately increased or decreased can be Examples related to the present invention as well.

The middle part of Table 1A represents each value of a wide angle end (WIDE), the middle of varying magnification (MID), and a telephoto end (TELE), i.e., distances between lens groups: D5, D13, D23, D28 and D32; f: the focal length of the entire lens system (unit mm of each value); Fno: F number; and 2ω: whole angles of view (in “°” units).

Further, the bottom part of Table 1A represents the focal length of each group. In this case, f₁: the focal length of the first lens group 1G, f₂: the focal length of the second lens group 2G, f₃: the focal length of the third lens group 3G, f₄: the focal length of the fourth lens group 4G, f₅: the focal length of the fifth lens group 5G, f_(3a): the focal length of the third-a lens group 3aG, and f_(3b): the focal length of the third-b lens group 3bG.

The term “the third-b group (OIS)” (OIS: Optical Image Stabilization) described in Table 1A represents being capable of achieving the performance of the camera shake correction function by allowing the third-b lens group 3bG to move in a direction perpendicular to the optical axis (in a direction to which X-Y plane extends).

TABLE 1A EXAMPLE 1 SURFACE GROUP NUMBER Ri Di Nj νj STRUCTURE  1 85.7554 1.950 1.84661 23.9 FIRST GROUP  2 62.5697 9.119 1.49700 81.5  3 −31126.9375 0.100  4 77.2118 4.299 1.61800 63.3  5 186.7731 D5  6 108.0235 1.350 1.88300 40.8 SECOND  7 18.6071 8.337 GROUP  8 −55.8960 1.000 1.88300 40.8  9 66.9403 0.700 10 37.4987 6.589 1.84661 23.9 11 −38.9747 0.362 12 −34.0881 1.000 1.75500 52.3 13 105.4506 D13 (APERTURE ∞ 1.000 THIRD- STOP) 14 a GROUP 15 33.7005 3.568 1.56732 42.8 16 −52.6106 0.363 17 28.4699 4.073 1.49700 81.5 18 −32.0211 0.900 1.90366 31.3 19 211.4451 2.505 *20  −67.2274 1.500 1.80348 40.4 THIRD-b 21 24.5327 1.041 GROUP (OIS) 22 27.2898 2.358 1.84661 23.9 23 69.3194 D23 *24  49.0350 4.377 1.51560 63.1 FOURTH *25  −43.0727 0.169 GROUP 26 46.1728 1.000 1.84661 23.9 27 22.9572 6.496 1.51680 64.2 28 −48.8859 D28 *29  85.0541 1.500 1.80348 40.4 FIFTH *30  20.5630 0.099 GROUP 31 19.5078 2.277 1.92286 20.9 32 25.9096 D32 33 ∞ 3.700 1.51680 64.2 Dg 34 ∞ WIDE MID TELE D5 0.950 32.298 66.596 D13 42.834 15.932 3.617 D23 12.578 6.213 3.622 D28 2.153 3.937 1.901 D32 35.505 66.444 82.661 f 18.384 67.549 248.190 Fno 3.60 5.48 6.49 2ω [°] 76.61 22.49 6.22 f₁ 111.303 f₂ −17.195 f₃ 89.768 f₄ 28.523 f₅ −59.029 f_(3a) 33.607 f_(3b) (OIS) −39.462

Table 1B shows aspheric coefficients of aspheric surfaces of the zoom lens of Example 1. In the lens data of Table 1A, the mark “*” attached to a surface number indicates that a surface represented by the surface number is an aspheric surface. Further, Table 1B shows the aspheric coefficients of aspheric surfaces corresponding to these surface numbers.

The aspheric coefficients represented in Table 1B are prepared to define aspheric shapes by being applied in the following aspheric equation. Z=C·h ²/{1+(1−K·C ² ·h ²)^(1/2) }+ΣAn·h ^(n)  [Aspheric Equation 1] where

-   Z: the depth of an aspheric surface (mm) -   h: the distance from the optical axis to a lens surface (height)     (mm) -   K: aspheric coefficients representing quadric surface -   C: paraxial curvature=1/R (R: paraxial curvature radius) -   An: n-dimensional (n is an integer not less than three) aspheric     coefficient

TABLE 1B ASPHERIC COEFFICIENT SURFACE NUMBER SIGN *20 *24 *25 *29 *30 K 1.000000E+00 1.000000E+00 1.000000E+00 1.000000E+00 1.000000E+00 A3 −6.660863E−06 2.113073E−05 1.195308E−05 6.668667E−07 1.051388E−05 A4 1.068409E−05 −1.787018E−05 9.213718E−07 −1.182857E−07 −3.423284E−06 A5 −6.114474E−07 −3.133994E−07 2.202715E−08 −9.254225E−09 7.184053E−07 A6 3.008719E−08 1.883512E−07 −6.561077E−10 −4.950193E−10 −1.065630E−08 A7 2.785752E−09 −2.494012E−08 −1.302087E−10 −1.901654E−11 −4.565539E−09 A8 −7.187710E−11 1.247161E−09 −1.087276E−11 −1.551834E−13 −1.629647E−11 A9 −1.749371E−11 9.724427E−14 −6.432469E−13 7.118640E−14 4.500121E−11 A10 5.214071E−13 −1.350450E−12 −2.148723E−14 1.063682E−14 −1.679259E−12 A11 −9.928876E−17 9.672666E−16 −1.039705E−15 1.136476E−15 1.043516E−15 A12 −1.891767E−16 1.223378E−17 −3.166091E−17 1.069028E−16 7.735059E−17 A13 −6.521684E−17 −4.164422E−18 1.294460E−18 9.376248E−18 6.733229E−18 A14 −1.390141E−17 −7.285136E−19 3.747765E−19 7.834346E−19 6.654046E−19 A15 −1.714540E−18 7.231878E−20 8.216610E−20 2.319643E−19 2.466336E−19 A16 −2.682522E−19 4.235680E−21 9.394894E−21 1.747560E−20 2.657868E−20

FIG. 7 is a diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at each of a wide angle end (WIDE), the middle of varying magnification (MID), and a telephoto end (TELE). Further, aberrations of each light beam of the d-line and the g-line are shown in the Figure. The diagram of astigmatism represents aberrations with respect to sagittal image surfaces and tangential image surfaces.

As shown in FIG. 7, diagrams indicated by the symbols Wa, Ma, and Ta represent spherical aberration, diagrams indicated by the symbols Wb, Mb, and Tb represent astigmatism, diagrams indicated by the symbols Wc, Mc, and Tc represent distortion, and diagrams indicated by the symbols Wd, Md, and Td represent lateral chromatic aberration.

Table 6 as shown at the end of the description of the Examples represents values (values evaluated from mathematical expression of formula (M)) of formula (M) for Examples 1 through 5, individually. The mathematical expression of each formula can be evaluated from various data and the like with respect to the zoom lenses in Tables 1A through 5A.

As can be seen from the above lens data and the like, the zoom lens of Example 1 has a high variable ratio, and yet is compact and capable of high performance.

FIGS. 2A and 2B illustrating a configuration of the zoom lens of Example 1, FIG. 7 illustrating aberrations of the zoom lens, Tables 1A & 1B representing the lens data and the like of the zoom lens, and Table 6 representing the values of each mathematical expression of formula (M) are read in the same manner as in Examples through 5 to be described later, and therefore detailed descriptions thereof will be omitted.

EXAMPLE 2

FIGS. 3A and 3B show a zoom lens of Example 2. FIG. 3A is a diagram illustrating the specific configuration of the zoom lens of Example 2. FIG. 3B is related to the zoom lens of Example 2, and illustrates a state in which the zoom setting is set to a wide angle end (as indicated by “WIDE” in the Figure) at the upper part and a state in which the zoom setting thereof is set to a telephoto end (as indicated by “TELE” in the Figure) at the bottom part. Further, arrows indicate the paths of movement of the lens groups, respectively when magnification is changed from the wide angle end to the telephoto end.

In the fifth lens group 5G of the zoom lens of Example 2, two lenses, i.e., a positive lens and a negative lens, are arranged in this order from the object side.

Further, Table 2A shows various data related to the zoom lens of Example 2. The upper part of Table 2A shows lens data, the middle part shows schematic specifications of the zoom lens, and the bottom part shows the focal length of each lens group.

TABLE 2A EXAMPLE 2 SURFACE GROUP NUMBER Ri Di Nj νj STRUCTUER  1 85.2292 2.520 1.84661 23.9 FIRST GROUP  2 61.7335 9.054 1.49700 81.5  3 −1963.5475 0.100  4 66.8404 4.168 1.60300 65.4  5 147.8987 D5  6 88.0438 1.400 1.88300 40.8 SECOND  7 18.3402 8.245 GROUP  8 −50.9539 1.050 1.83481 42.7  9 63.5833 1.045 10 37.5330 6.423 1.84661 23.9 11 −37.5330 0.405 12 −32.6020 1.050 1.77250 49.6 13 97.2521 D13 (APERTURE ∞ 1.000 THIRD-a STOP) 14 GROUP 15 33.0761 3.238 1.54814 45.8 16 −58.1129 0.218 17 29.9896 4.828 1.49700 81.5 18 −29.9896 0.900 1.85026 32.3 19 200.1256 4.148 *20  −64.3421 1.500 1.80168 40.7 THIRD-b *21  24.7941 0.835 GROUP (OIS) 22 27.9314 2.293 1.84661 23.9 23 67.4658 D23 *24  52.0924 4.603 1.51530 62.8 FOURTH *25  −41.7940 0.118 GROUP 26 48.9063 1.050 1.75520 27.5 27 23.5612 5.631 1.48749 70.2 28 −52.7318 D28 29 −77.6900 2.362 1.80518 25.4 FIFTH 30 −34.1433 1.323 GROUP *31  −38.3946 1.500 1.80168 40.7 *32  175.1091 D32 33 ∞ 5.200 1.51680 64.2 Dg 34 ∞ WIDE MID TELE D5 0.900 34.251 61.985 D13 43.622 17.798 3.965 D23 10.401 5.906 3.496 D28 3.770 5.315 1.700 D32 33.109 60.979 85.617 f 18.388 67.562 248.238 Fno 3.60 5.18 6.47 2ω [°] 76.59 22.60 6.27 f₁ 105.536 f₂ −16.856 f₃ 97.458 f₄ 29.520 f₅ −84.482 f_(3a) 35.192 f_(3b) (OIS) −37.423

Table 2B shows aspheric coefficients of aspheric surfaces of the zoom lens of Example 2.

TABLE 2B ASPHERIC COEFFICIENT SURFACE NUMBER SIGN *20 *21 *24 *25 *31 *32 K  1.000000E+00  1.000000E+00  1.000000E+00  1.000000E+00  1.000000E+00  1.000000E+00 A3 −6.214685E−06  1.210237E−06  2.670345E−05  1.418960E−05 −6.078072E−06  7.219238E−07 A4  1.178008E−05 −2.059917E−07 −1.699876E−05  3.117539E−07 −8.397924E−08 −1.310513E−07 A5 −5.734545E−07 −7.148778E−09 −2.869234E−07  2.819776E−09 −3.195286E−07 −3.857289E−09 A6  2.988894E−08  1.380535E−10  1.883256E−07 −7.772038E−10 −4.462125E−09 −5.848393E−10 A7  2.617898E−09  2.608762E−11 −2.502808E−08 −9.142656E−11  2.561994E−09 −7.783658E−11 A8 −9.134118E−11  1.435216E−13  1.237420E−09 −6.908198E−12  7.007254E−11 −7.925124E−12 A9 −1.920589E−11 −3.192440E−13 −6.986446E−13 −4.003267E−13 −2.680817E−11 −7.016044E−13 A10  3.923019E−13 −5.843137E−14 −1.406596E−12 −1.483360E−14  9.907504E−13 −5.825802E−14 A11 −7.929852E−15 −7.084585E−15 −2.653633E−15 −1.835598E−15 −9.622458E−15 −4.777413E−15 A12 −6.308512E−16 −6.646965E−16 −2.176749E−16 −2.125550E−16 −9.379487E−16 −4.039401E−16 A13 −5.271484E−17 −4.473916E−17 −2.116950E−17 −2.258551E−17 −8.488742E−17 −3.628087E−17 A14 −2.605892E−18 −6.306065E−19 −2.497013E−18 −2.231667E−18 −7.080190E−18 −3.496352E−18 A15  1.622770E−18  4.767090E−19 −2.199383E−19 −3.898770E−19 −6.276121E−19 −8.095367E−19 A16  3.760341E−19  1.155446E−19 −2.569275E−20 −4.124631E−20 −3.345415E−20 −9.331008E−20

FIG. 8 is a diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at each of a wide angle end (WIDE), the middle of varying magnification (MID), and a telephoto end (TELE) of the zoom lens of Example 2.

EXAMPLE 3

FIGS. 4A and 4B show a zoom lens of Example 3. FIG. 4A is a diagram illustrating the specific configuration of the zoom lens of Example 3. FIG. 4B is related to the zoom lens of Example 3, and illustrates a state in which the zoom setting is set to a wide angle end (as indicated by “WIDE” in the Figure) at the upper part and a state in which the zoom setting thereof is set to a telephoto end (as indicated by “TELE” in the Figure) at the bottom part. Further, arrows indicate the paths of movement of the lens groups, respectively when magnification is changed from the wide angle end to the telephoto end.

In the fifth lens group 5G of the zoom lens of Example 3, two lenses, i.e., a positive lens and a negative lens, are arranged in this order from the object side.

Further, Table 3A shows various data related to the zoom lens of Example 3. The upper part of Table 3A shows lens data, the middle part shows schematic specifications of the zoom lens, and the bottom part shows the focal length of each lens group.

TABLE 3A EXAMPLE 3 SURFACE GROUP NUMBER Ri Di Nj νj STRUCTURE  1 86.1227 1.650 1.84661 23.9 FIRST GROUP  2 62.0701 9.553 1.49700 81.5  3 −4250.8858 0.200  4 69.0201 5.134 1.61800 63.3  5 173.7706 D5  6 143.9195 1.250 1.88300 40.8 SECOND  7 17.9097 8.359 GROUP *8 −54.1875 0.200 1.52771 41.8  9 −52.5929 1.000 1.80400 46.6 10 61.2864 1.229 11 38.6886 5.875 1.84661 23.9 12 −38.4723 1.010 1.80400 46.6 13 99.9343 D13 (APERTURE ∞ 1.000 THIRD-a STOP) 14 GROUP 15 32.7747 3.500 1.54814 45.8 16 −52.1190 1.172 17 28.6007 4.608 1.49700 81.5 18 −31.7142 1.000 1.90366 31.3 19 247.9630 2.532 *20  −62.9067 1.500 1.80348 40.4 THIRD-b 21 24.4096 1.000 GROUP (OIS) 22 26.9299 2.518 1.84661 23.9 23 65.6490 D23 *24  49.2954 4.978 1.51560 63.1 FOURTH *25  −44.8007 1.459 GROUP 26 47.4064 0.900 1.84661 23.9 27 23.0755 6.115 1.51680 64.2 28 −45.9160 D28 29 −225.5534 2.848 1.84661 23.9 FIFTH 30 −35.6067 0.500 GROUP *31  −39.1114 1.500 1.80348 40.4 *32  54.4009 D32 33 ∞ 3.700 1.51680 64.2 Dg 34 ∞ WIDE MID TELE D5 0.999 31.879 61.061 D13 42.746 17.373 4.203 D23 11.516 5.965 3.499 D28 1.951 3.394 1.885 D32 35.490 64.031 78.012 f 18.382 64.988 229.769 Fno 3.62 5.22 6.08 2ω [°] 76.61 23.33 6.73 f₁ 103.033 f₂ −16.513 f₃ 87.566 f₄ 29.127 f₅ −66.647 f_(3a) 33.407 f_(3b) (OIS) −37.492

Table 3B shows aspheric coefficients of aspheric surfaces of the zoom lens of Example 3.

TABLE 3B ASPHERIC COEFFICIENT SURFACE NUMBER SIGN *8 *20 *24 *25 *31 *32 K 1.464546E+00  1.000000E+00 1.000000E+00  1.000000E+00  1.000000E+00  1.000000E+00 A3 0.000000E+00 −6.784837E−06 2.196427E−05  1.195660E−05 −1.149323E−05 −1.143922E−06 A4 2.212057E−06  1.073941E−05 −1.784348E−05   8.656127E−07 −3.692099E−07  8.049956E−10 A5 0.000000E+00 −6.120021E−07 −3.189917E−07   2.476411E−08 −3.237427E−07 −3.487018E−10 A6 −8.509320E−09   2.983909E−08 1.875408E−07 −4.076491E−11 −4.237706E−09 −1.612101E−10 A7 0.000000E+00  2.765409E−09 −2.501350E−08  −6.934857E−11  2.612386E−09 −2.141371E−11 A8 1.827402E−11 −7.300686E−11 1.241716E−09 −6.189639E−12  7.725014E−11 −1.924803E−12 A9 0.000000E+00 −1.754200E−11 −2.534825E−13  −3.333725E−13 −2.592973E−11 −1.269553E−13 A10 −1.356278E−13   5.200665E−13 −1.369651E−12  −3.716054E−15  1.087591E−12 −4.597426E−15 A11  4.577131E−17 2.121105E−16 −2.243534E−16  2.093262E−16  3.219858E−16 A12 −1.519797E−16 1.643937E−17 −1.434839E−17 −8.269620E−18  9.836844E−17 A13 −5.440776E−17 1.428068E−18 −9.633478E−19 −2.966776E−18  1.494300E−17 A14 −1.137249E−17 1.494776E−19 −8.031938E−20 −4.355006E−19  1.856954E−18

FIG. 9 is a diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at each of a wide angle end (WIDE), the middle of varying magnification (MID), and a telephoto end (TELE) of the zoom lens of Example 3.

EXAMPLE 4

FIGS. 5A and 5B show a zoom lens of Example 4. FIG. 5A illustrates the specific configuration of the zoom lens of Example 4. FIG. 5B is related to the zoom lens of Example 4, and illustrates a state in which the zoom setting is set to a wide angle end (as indicated by “WIDE” in the Figure) at the upper part and a state in which the zoom setting thereof is set to a telephoto end (as indicated by “TELE” in the Figure) at the bottom part. Further, arrows indicate the paths of movement of the lens groups, respectively when magnification is changed from the wide angle end to the telephoto end.

In the fifth lens group 5G of the zoom lens of Example 4, two lenses, i.e., a positive lens and a negative lens, are arranged in this order from the object side.

Further, Table 4A shows various data related to the zoom lens of Example 4. The upper part of Table 4A shows lens data, the middle part shows schematic specifications of the zoom lens, and the bottom part shows the focal length of each lens group.

TABLE 4A EXAMPLE 4 SURFACE GROUP NUMBER Ri Di Nj νj STRUCTURE  1 84.9463 1.950 1.84661 23.9 FIRST GROUP  2 62.2446 8.693 1.49700 81.5  3 ∞ 0.100  4 68.3452 4.363 1.60300 65.4  5 153.8323 D5  6 89.2120 1.350 1.88300 40.8 SECOND  7 18.2963 8.233 GROUP  8 −58.1632 1.000 1.88300 40.8  9 67.7426 0.948 10 37.5173 6.506 1.84661 23.9 11 −38.5206 0.408 12 −33.7911 1.000 1.77250 49.6 13 99.4178 D13 (APERTURE ∞ 1.000 THIRD-a STOP) 14 GROUP 15 33.6716 3.293 1.51742 52.4 16 −58.3051 0.100 17 28.2935 4.126 1.49700 81.5 18 −31.9738 0.900 1.83400 37.2 19 127.3405 2.569 20 −68.3981 2.272 1.84661 23.9 THIRD-b 21 −26.8082 0.886 GROUP (OIS) 22 −24.8406 1.500 1.80348 40.4 *23  62.6811 D23 *24  49.8918 4.452 1.51560 63.1 FOURTH *25  −42.8733 0.100 GROUP 26 53.2553 1.000 1.80518 25.4 27 23.3404 5.973 1.51823 58.9 28 −46.7603 D28 29 −81.9572 2.357 1.80518 25.4 FIFTH 30 −34.7267 1.493 GROUP *31  −38.2183 1.500 1.80348 40.4 *32  179.9979 D33 33 ∞ 4.900 1.51680 64.2 Dg 34 ∞ WIDE MID TELE D5 0.900 33.799 63.266 D13 44.713 17.634 3.566 D23 11.185 6.816 4.357 D28 3.245 4.848 1.970 D32 34.996 63.954 86.941 f 18.366 67.481 247.941 Fno 3.60 5.26 6.55 2ω [°] 76.64 22.68 6.28 f₁ 107.872 f₂ −17.446 f₃ 116.489 f₄ 29.082 f₅ −85.750 f_(3a) 37.832 f_(3b) (OIS) −39.192

Table 4B shows aspheric coefficients of aspheric surfaces of the zoom lens of Example 4.

TABLE 4B ASPHERIC COEFFICIENT SURFACE NUMBER SIGN *23 *24 *25 *31 *32 K 1.000000E+00 1.000000E+00 1.000000E+00 1.000000E+00 1.000000E+00 A3 1.288744E−05 2.647809E−05 1.085607E−05 −7.403052E−06 −1.039624E−07 A4 −1.078292E−05 −1.725827E−05 4.339778E−07 −1.719981E−07 −1.241135E−07 A5 6.382901E−07 −2.955264E−07 7.445503E−09 −3.195104E−07 −6.411543E−09 A6 −2.635804E−08 1.884390E−07 −7.830304E−10 −4.172605E−09 −7.019777E−10 A7 −2.463874E−09 −2.498717E−08 −1.006144E−10 2.599459E−09 −6.791905E−11 A8 9.303492E−11 1.241227E−09 −7.050127E−12 7.428064E−11 −5.579190E−12 A9 1.836592E−11 −4.496962E−13 −3.044782E−13 −2.634935E−11 −4.226272E−13 A10 −5.521081E−13 −1.394620E−12 3.515842E−15 1.038713E−12 −3.175412E−14 A11 −1.312550E−14 −2.307759E−15 5.035691E−16 −4.914561E−15 −2.523663E−15 A12 −1.649716E−15 −2.136162E−16 3.668331E−17 −5.118335E−16 −2.219919E−16 A13 −1.438455E−16 −1.859723E−17 1.097923E−18 −5.040249E−17 −2.163300E−17 A14 −6.585779E−18 −1.568050E−18 −1.859078E−19 −4.774574E−18 −2.263951E−18 A15 −4.147342E−19 −2.121945E−20 −2.309610E−19 −5.390733E−19 −6.968129E−19 A16 1.147946E−19 8.062655E−21 −3.078231E−20 −4.101269E−20 −8.198580E−20

FIG. 10 is a diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at each of a wide angle end (WIDE), the middle of varying magnification (MID), and a telephoto end (TELE) of the zoom lens of Example 4.

EXAMPLE 5

FIGS. 6A and 6B show a zoom lens of Example 5. FIG. 6A illustrates the specific configuration of the zoom lens of Example 5. FIG. 6B is related to the zoom lens of Example 5, and illustrates a state in which the zoom setting is set to a wide angle end (as indicated by “WIDE” in the Figure) at the upper part and a state in which the zoom setting thereof is set to a telephoto end (as indicated by “TELE” in the Figure) at the bottom part. Further, arrows indicate the paths of movement of the lens groups, respectively when magnification is changed from the wide angle end to the telephoto end.

In the fifth lens group 5G of the zoom lens of Example 5, two lenses, i.e., a positive lens and a negative lens, are arranged in this order from the object side.

Further, Table 5A shows various data related to the zoom lens of Example 5. The upper part of Table 5A shows lens data, the middle part shows schematic specifications of the zoom lens, and the bottom part shows the focal length of each lens group.

TABLE 5A EXAMPLE 5 SURFACE GROUP NUMBER Ri Di Nj νj STRUCTURE  1 85.2992 2.520 1.84661 23.9 FIRST GROUP  2 61.8500 9.114 1.49700 81.5  3 −2375.7864 0.100  4 66.8941 4.269 1.60300 65.4  5 146.5034 D5  6 87.8998 1.400 1.88300 40.8 SECOND  7 18.3570 8.315 GROUP  8 −51.0001 1.050 1.83481 42.7  9 63.6139 0.815 10 37.4113 6.407 1.84666 23.8 11 −37.4113 0.388 12 −32.5753 1.050 1.77250 49.6 13 98.4906 D13 (APERTURE ∞ 1.100 THIRD-a STOP) 14 GROUP 15 34.2381 3.329 1.54814 45.8 16 −60.1143 0.937 17 27.0475 4.232 1.49700 81.5 18 −33.1140 0.900 1.85026 32.3 19 163.6420 3.836 *20  −63.3026 1.500 1.80168 40.7 THIRD-b *21  24.7365 0.864 GROUP (OIS) 22 28.0299 2.277 1.84666 23.8 23 66.7227 D23 *24  52.7776 4.675 1.51530 62.8 FOURTH *25  −42.2885 0.105 GROUP 26 48.3349 1.050 1.75520 27.5 27 23.5950 5.625 1.48749 70.2 28 −52.9320 D28 29 −77.2285 2.360 1.80518 25.4 FIFTH 30 −34.0317 1.053 GROUP *31  −38.4236 1.500 1.80168 40.7 *32  175.0302 D32 33 ∞ 5.200 1.51680 64.2 Dg 34 ∞ WIDE MID TELE D5 0.900 36.423 62.766 D13 43.473 17.944 3.610 D23 10.708 6.338 3.715 D28 3.842 5.548 1.698 D32 33.106 58.073 84.416 f 18.389 67.564 248.247 Fno 3.62 5.02 6.39 2ω [°] 76.66 22.61 6.27 f₁ 106.443 f₂ −16.902 f₃ 94.599 f₄ 29.607 f₅ −84.036 f_(3a) 34.301 f_(3b) (OIS) −36.710

Table 5B shows aspheric coefficients of aspheric surfaces of the zoom lens of Example 5.

TABLE 5B ASPHERIC COEFFICIENT SURFACE NUMBER SIGN *20 *21 *24 *25 *31 *32 K  1.000000E+00  1.000000E+00  1.000000E+00  1.000000E+00  1.000000E+00  1.000000E+00 A3 −6.165192E−06  1.136414E−06  2.646484E−05  1.455922E−05 −5.608010E−06  3.111280E−07 A4  1.180918E−05 −2.391292E−07 −1.700884E−05  3.247792E−07 −6.243737E−08 −1.509737E−07 A5 −5.712797E−07 −9.755106E−09 −2.879359E−07  3.790736E−09 −3.186333E−07 −4800208E−09 A6  3.004106E−08 −5.784070E−11  1.882504E−07 −7.189621E−10 −4.429101E−09 −6.392048E−10 A7  2.628840E−09  1.065292E−11 −2.503214E−08 −8.915027E−11  2.562357E−09 −8.139704E−11 A8 −9.058174E−11 −1.062813E−12  1.237303E−09 −6.929168E−12  6.993044E−11 −8.143708E−12 A9 −1.916284E−11 −4.032273E−13 −6.914544E−13 −4.165896E−13 −2.683328E−11 −7.108067E−13 A10  3.931210E−13 −6.248737E−14 −1.404954E−12 −1.706208E−14  9.877237E−13 −5.801155E−14 A11 −8.205763E−15 −6.993822E−15 −2.471879E−15 −2.065580E−15 −9.923479E−15 −4.652135E−15 A12 −6.918798E−16 −6.032048E−16 −2.028307E−16 −2.332995E−16 −9.630020E−16 −3.833882E−16 A13 −6.145538E−17 −3.361798E−17 −2.032344E−17 −2.430529E−17 −8.645582E−17 −3.363706E−17 A14 −3.613976E−18  8.786762E−19 −2.491248E−18 −2.366453E−18 −7.105990E−18 −3.193681E−18 A15  1.528779E−18  6.479148E−19 −2.276198E−19 −4.001489E−19 −6.139199E−19 −7.773001E−19 A16  3.702179E−19  1.315589E−19 −2.724708E−20 −4.204166E−20 −3.018856E−20 −9.005424E−20

FIG. 11 is a diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at each of a wide angle end (WIDE), the middle of varying magnification (MID), and a telephoto end (TELE) of the zoom lens of Example 5.

The zoom lens of Example 5, which is constructed in such a manner, can have a high variable magnification ratio, and yet be compact and capable of high performance.

TABLE 6 EXAM- EXAM- EXAM- EXAM- PLE 1 PLE 2 PLE 3 PLE 4 EXAMPLE 5 FORMULA (M) −0.852 −0.940 −0.891 −0.965 −0.934

The above zoom lens may have the following configuration. All of the zoom lenses of the above Examples 1 through 5 are assumed to have the configuration as shown below.

It should be noted that in the zoom lens of the present invention, the fifth lens group 5G has at least one aspheric surface, and that it is desirable for the zoom lens to satisfy formula (A): 10<ν_(5n)−ν_(5p)<30 and formula (B): 1.77<N_(5n), at the same time, and it is more desirable for the zoom lens to satisfy formula (A′): 12<ν_(5n)−ν_(5p)<25 and/or formula (B′): 1.79<N_(5n).

In this case, ν_(5n) is an average value of the Abbe number (based on the d-line) of each lens having negative refractive power, which constitute the fifth lens group 5G; ν_(5p) is an average value of the Abbe number (based on the d-line) of each lens having positive refractive power, which constitute the fifth lens group 5G; and N_(5n) is an average value of the refractive index (with respect to the d-line) of each lens having negative refractive power, which constitute the fifth lens group 5G.

As described above, if the fifth lens group has at least one aspheric surface, performance variations can be favorably suppressed at the time of focusing.

Formula (A) regulates the Abbe number with respect to the d-line of a negative lens and a positive lens that constitute the fifth lens group 5G. If the zoom lens is constructed in such a manner that the value of ν_(5n)−ν_(5p) is lower than the lower limit defined by formula (A), correction for chromatic aberration within the fifth lens group 5G will be insufficient, and chromatic aberration will become a problem at the time of focal shift. Meanwhile, if the zoom lens is constructed in such a manner that the value of ν_(5n)−ν_(5p) exceeds the upper limit defined by formula (A), correction for chromatic aberration within the fifth lens group 5G is sufficient, but the refractive index of the negative lens will be forced to be small. This will cause a problem that the curvature of image field of a peripheral image will become large.

Formula (B) regulates the refractive index with respect to the d-line of a negative lens within the fifth lens group 5G. If the zoom lens 100 is constructed in such a manner that the value of N_(5n) is lower than the lower limit defined by formula (B), a refractive index of the negative lens within the fifth lens group 5G becomes too small, which will cause a problem that the curvature of image field of a peripheral image will become more likely to occur.

Further, it is desirable for the zoom lens to satisfy formula (C): −0.6<1−β_(5T) ²<−2.5, and more desirably, formula (C′): −5.5<1−β_(5T) ²<−2.9.

β_(5T) is an image formation magnification of the fifth lens group 5G when focusing on infinity at the telephoto end.

Formula (C) regulates the sensitivity to image shift with respect to a focal shift at the time of focusing on infinity at the telephoto end in the fifth lens group 5G. If the zoom lens 100 is constructed in such a manner that the value of 1−β_(5T) ² is lower than the lower limit defined by formula (C), the sensitivity to the image shift with respect to the focal shift of the fifth lens group 5G at the telephoto end will be excessively increased, which will cause the amount of amplitude shift of the fifth lens group 5G for finding the best point of focus to be excessively reduced. As a result, problems such that it will become difficult to perform focus control, for example, the focal shift of the fifth lens group 5G becoming suspended, will arise. If the zoom lens 100 is constructed in such a manner that the value of 1−β_(5T) ² exceeds the upper limit defined by formula (C), the sensitivity of the image shift with respect to the focal shift of the fifth lens group 5G will be acceptable at the telephoto end, but the sensitivity at the wide angle end will be excessively reduced. This will cause the amount of amplitude shift of the fifth lens group 5G for finding the best point of focus to be excessively increased. As a result, for example, problems, that abnormal noises are made by the focusing mechanism at the time of the focus shift, will arise.

The fifth lens group 5G comprises a positive lens and a negative lens, and it is desirable to arrange the positive lens and the negative lens in this order from the object side. This enables the fifth lens group 5G to be constituted by the requisite minimum number of lenses which can suppress performance variations at the time of focusing, thereby reducing the burden on the focusing mechanism and achieving high-speed focus. Further, the arrangement of the positive lens and the negative lens in this order from the object side facilitates divergence of reflection on each lens surface for a light beam which is reflected on the imaging surface of the imaging element and which returns to the fifth lens group 5G because more convex surfaces of the lenses constituting the fifth lens group 5G face toward the image side. This reduces the generation of eye-catching ghost images.

That is, it is desirable for the above zoom lens to satisfy formula (D): 0.10<f_(w)/f₁<0.25; and more desirably, formula (D′): 0.15<f_(w)/f₁<0.20, where f_(w) is the focal length of the entire lens system at a wide angle end and f₁ is the focal length of the first lens group 1G.

Formula (D) regulates the ratio of the focal length of the entire lens system at a wide angle end to the focal length of the first lens group 1G. If the zoom lens is constructed in such a manner that the value of f_(w)/f₁ is less than the lower limit defined by formula (D), the focal length of the first lens group 1G becomes too large, which causes a problem that the outer diameters of the lenses of the first lens group 1G and the total length of the optical system will become great at the telephoto end. If the zoom lens is constructed in such a manner that the value of f_(w)/f₁ exceeds the upper limit defined by formula (D), positive refractive power of the first lens group 1G becomes too strong, which will cause a problem that it becomes difficult to maintain optical performance at the telephoto end.

Further, it is desirable for the zoom lens to satisfy formula (F): −1.5<f_(w)/f₂<−0.5, and more desirably, formula (F′): −1.2<f_(w)/f₂<−1.0, where F₂ is the focal length of a second lens group 2G.

Formula (F) regulates the ratio of the focal length of the entire lens system at a wide angle end to the focal length of the second lens group 2G. If the zoom lens is constructed in such a manner that the value of f_(w)/f₂ is lower than the lower limit defined by formula (F), negative refractive power of the second lens group 2G will be excessively increased, which will cause a problem that the curvature of image field of a peripheral image will become large. Further, a problem of difficulties in maintaining optical performance when magnification is varied will also occur. If the zoom lens is constructed in such a manner that the value of f_(w)/f₂ exceeds the upper limit defined by formula (F), negative refractive power of the second lens group 2G will be excessively reduced, which will increase the amount of shift of the first lens group 1G when magnification is varied. This will cause a problem that the outer diameters of the lenses of the first lens group 1G and the total length of the optical system will become great at the telephoto end.

Further, it is desirable for the zoom lens to satisfy formula (H): 0.10<f_(w)/f₃<0.50, and more desirably, formula (H′): 0.15<f_(w)/f₃<0.30, where f₃ is the focal length of a third lens group 3G.

Formula (H) regulates the ratio of the focal length of the entire lens system at a wide angle end to the focal length of the third lens group 3G. If the zoom lens is constructed in such a manner that the value of f_(w)/f₃ is lower than the lower limit defined by formula (H), positive refractive power of the third lens group 3G will be excessively reduced, which will increase the amount of shift of the third lens group 3G when magnification is varied. This causes a problem that the total length of the optical system grows to a large size. If the zoom lens is constructed in such a manner that the value of f_(w)/f₃ exceeds the upper limit defined by formula (H), positive refractive power of the third lens group 3G will be excessively increased. This will cause a problem of difficulties in maintaining optical performance when magnification is varied.

Further, it is desirable for the zoom lens to satisfy formula (J): 0.50<f_(w)/f₄<0.65 and formula (K): −0.32<f_(w)/f₅<−0.15 at the same time, and more desirably, formula (J′): 0.60<f_(w)/f₄<0.65 and/or formula (K′): −0.32<f_(w)/f₅<−0.20, where f₄ is the focal length of the fourth lens group 4G and f₅ is the focal length of the fifth lens group 5G.

Formula (J) regulates the ratio of the focal length of the entire lens system at a wide angle end to the focal length of the fourth lens group 4G. If the zoom lens is constructed in such a manner that the value of f_(w)/f₄ is lower than the lower limit defined by formula (J), positive refractive power of the fourth lens group 4G will be excessively reduced, which will increase the amount of shift of the fourth lens group 4G when magnification is varied. This will cause a problem that the total length of the optical system will become great. If the zoom lens is constructed in such a manner that the value of f_(w)/f₄ exceeds the upper limit defined by formula (J), positive refractive power of the fourth lens group 4G will be excessively increased. This will cause a problem of difficulties in maintaining optical performance when magnification is varied.

Formula (K) regulates the ratio of the focal length of the entire lens system at a wide angle end to the focal length of the fifth lens group 5G. If the zoom lens is constructed in such a manner that the value of f_(w)/f₅ is lower than the lower limit defined by formula (K), negative refractive power of the fifth lens group 5G will be excessively increased, which will causes a problem that the back focus length will becomes longer and the entire length of the optical system will become great. If the zoom lens is constructed in such a manner that the value of f_(w)/f₅ exceeds the upper limit defined by formula (K), negative refractive power of the fifth lens group 5G will be excessively reduced, which will diminish the back focus length. This will cause a problem that spaces for a mirror of a single-lens reflex camera, a filter, and the like cannot be secured, for example. In addition, the amount of shift of the fifth lens group 5G will be increased at the time of focus, and further the outer diameters of the lenses of the fifth lens group 5G will become great. This increases the burden on the focusing mechanism so that it will become difficult to achieve high-speed focus, for example.

The present invention is not limited to the embodiments and the examples described above, and various modifications are possible. For example, values, such as the radius of curvature of each lens element, distances between surfaces, and refractive indices, are not limited to the values in the numerical examples shown in the Tables, but may be other values. 

What is claimed is:
 1. A zoom lens, substantially consisting of: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; a fourth lens group having positive refractive power; and a fifth lens group having negative refractive power, which are arranged in this order from an object side of the zoom lens, wherein when varying magnification from a wide angle end to a telephoto end, the distance between the first lens group and the second lens group is consistently increased, the distance between the second lens group and the third lens group is consistently decreased, the distance between the third lens group and the fourth lens group is consistently decreased, and the distance between the fourth lens group and the fifth lens group is changed, while all of the lens groups are moved with respect to an image formation position, wherein when moving a point of focus from an infinity side to a near side to achieve focus, only the fifth lens group is moved to the image side, wherein the third lens group comprises a third-a lens group having positive refractive power and a third-b lens group having negative refractive group, which are arranged in this order from the object side, only the third-b lens group is moved in a direction perpendicular to the optical axis to achieve camera shake correction, and the following formula (M) is satisfied: −2.00<f _(3a) /f _(3b)<−0.85  (M), where f_(3a): the focal length of the third-a lens group, and f_(3b): the focal length of the third-b lens group.
 2. The zoom lens as defined in claim 1, wherein the following formula (M′) is satisfied: −1.00<f _(3a) /f _(3b)<−0.85  (M′) f_(3a): the focal length of the third-a lens group, and f_(3b): the focal length of the third-b lens group.
 3. The zoom lens as defined in claim 1, wherein the third-b lens group comprises one negative lens and one positive lens.
 4. The zoom lens as defined in claim 1, wherein the third-b lens group comprises two single lenses and has at least one aspheric surface.
 5. The zoom lens as defined in claim 2, wherein the third-b lens group comprises one negative lens and one positive lens.
 6. The zoom lens as defined in claim 2, wherein the third-b lens group comprises two single lenses and has at least one aspheric surface.
 7. An imaging apparatus comprising: the zoom lens as defined in claim
 1. 